AGM battery and fridge issues

[Redtail]

Have I killed my AGM battery box? And what's going on with my fridge?

In April 2019, I built an auxiliary battery box with a 90Ah Bosch M4 High Cycle Marine (HCM27-750). It gets charged as the third battery with the Traxide kit in my D4, or via a Victron Blue Smart 5A charger when it's on the shelf. It's been working fine, until ...

Left it in the garage for a month now, before connecting to the AC charger 5 days ago in anticipation of this weekend's trip.
It's been sitting at 13.1V all week. Disconnected it, dropped in the missus' RAV4, connected fridge to the battery box and AC power to keep the fridge running overnight.

Here's the graph from last night, and you can see where I loaded the car after 5pm.

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And today. Not only did the battery appear to be providing power, but it took a nosedive around 4am, eventually getting below the cut-off of 11.6V which of course shut down the fridge. (The battery box has a Traxide ABG25 in it.)

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So, why would the battery be supplying power when the Engel is plugged into the AC?
Power didn't go off overnight, and the fridge restarted when I disconnected and reconnect AC power this morning to test it.
The battery box did not want to supply anything.

Is the Engel AC/DC switch buggered and could it have been using battery?

And the other thing I just discovered is that the battery was sitting at 9.95V before I put it on charge last Saturday.
(Yeah, I should have checked it then!)
The Victron seems to have brought it back, but have I knackered it now?

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For now, the battery box is back on AC charge via the Victron. I'll know later today how it's fared.

[trout1105]

I will await drivesafes ideas here But my insticts are telling me that your 90AH battery is cactus unfortunately from the information that you have posted.

[towe0609]

I think you're likely up for a new battery too.

I've only recently started using these ... so make no claims about their long term service life ... but for me they are locally available and the right price per Kg/Ah

https://www.kmart.com.au/product/rechargeable-deep-cycle-agm-battery-80ah-12v-42963905/

I've had 2 in my camper for the last couple of months, servicing a fridge on 24/7 with daily solar charging - so far, so good.

[Redtail]

Thanks for the replies so far.

Having done a bit more research, I am finding myself agreeing that the battery may be stuffed.
I thought it was running down, powering the fridge, but looking at past graphs, I can see the curve is quite different. When the fridge is running, the compressor cycle is clearly visible in the shape of the line. The graphs above just show a fairly smooth line in comparison, which makes me think there's nothing wrong with the Engel (DC/AC auto switch) after all.

Looks like I'm going to have to use an esky to keep the beer cold this weekend.

[drivesafe]

Hi Redtail and with a starting voltage of just 9.95v, my guess is that your battery has dropped a cell.

Try recharging it again and you may be lucky but I suspect it is cactus.

[RobMichelle]

I know the fridges can be ran either off 12 or 240 but have never had em plugged in both at the same time ?

[PhilipA]

I do it all the time. The 2000 Engel auto changes to 240AC.
I also now run a 6amp 240/12DC 6amp charger into the line between battery and fridge with no ill effects so far.
Rather than running just the fridge on 240AC.
This charges the battery and runs the fridge. Only do this as the merit plug in the back of the car is convenient.
Regards PhilipA
I don't know if the fridge is reliable yet as it has only been used for 22 years.

[trout1105]

I know the fridges can be ran either off 12 or 240 but have never had em plugged in both at the same time ?

Most 12v fridges will swap over to 12v when the 240v power is turned off , I ALWAYS leave Both leads connected when using Engel, Primus or Waco fridges [thumbsupbig]

[RobMichelle]

Oh well I’m the odd one out then! [emoji106]

[Redtail]

Okay, second charge gave same result. Wouldn't hold a charge overnight, no load connected.
The voltage curve looks like an exact copy of the first one.
Looks like a new battery for me.
Happy to take recommendations in the 90/100Ah range. Current one is a Bosch M4 AGM. Maybe an SSB Dry Cell will work?

And to be doubly annoying, the little 25Ah iTech box I inherited recently, refused to work on DC, which is the recommended setting for the Engel. Instead, it ran for a good day and a half from its AC socket. Not bad.